Thanks fieldmarshaldj.
If the Grand Canyon is, say, forty million years old and Ice Ages occur, say, every forty thousand years, then the Grand Canyon must have been covered with ice over a thousand times in its history. Odd that the Colorado River can leave its mark, but being covered by an ice pack a mile thick a thousand times -- for centuries at a time -- does not. [JoeSchem]
Well, that's what I tell myself.
When was this guy Joe Schem writing? I thought the Ice Ages were around 100k apart not 40k, and only for about the last million years. The article said this covering by ice was half a billion years ago. I doubt Grand Canyon was covered by ice in these past million years.